Practical

Miscellaneous Practical Details

Below are some miscellaneous notes from the operation of Nzi traps in a residential setting in Russell, Ontario. Home use is straightforward, with minimal maintenance required.

Catch of Non-target Insects
Effect of Trap Height
Capturing Male Tabanidae

Catch of Non-target Insects

In initial trapping during 2001, I identified every insect captured. Non-biting species accounted for 83.6% of the catch. Flesh flies, Anthomyiidae flies, blow flies and small moths made up the majority of the catch. There was greater diversity relative to counts from a dry prairie environment in Alberta. Home, garden and crop insects dominated. From casual observations since then, catches of non-target insects differ considerably among years. The year 2001 had a particularly high catch of non-target insects.

	Lepidoptera consisted of many cabbage butterflies and some sulphurs, along with small moths. Few large species were captured.
	Hymenoptera consisted of wasps and bees, with only a few honey bees. No commercial honey production occurs nearby. Yellow jackets were common.
	Late in the season, catches of Coleoptera included many Asian ladybird beetles, and catches of Calliphoridae included many cluster flies.
	Muscidae were not common. No Musca domestica, and only a few M. autumnalis (face flies) were captured. Face flies are pests of local livestock, especially horses, but are not abundant in residential areas.
	Some predatory flies were caught in modest numbers. This is reflected in the catch of robber flies (Asilidae) and Mydaeinae.

Asian Ladybird Beetles

In 2004, I started to experiment with painted plywood traps. In autumn, I now routinely catch many Asian ladybird beetles (Harmonia axyridis) in this style of trap. To date, I have caught as many as 470 in one trap in one day (Nov 5, 2005 in a trap with an acrylic back, rather than a white polyester netting back). High catches occur only when farmers have harvested the soybean crop and winter is approaching (e.g. October +). The ladybugs are biting people at this time and are quite a nuisance. They are out in amazing numbers on warm, sunny days. They also get caught in cloth Nzi traps, but the catches are much higher in plywood traps, especially with the use of certain transparent materials in place of mosquito netting..

About 2,500 ladybugs caught over two days in autumn 2005 in 4 plywood and 2 cloth Nzi traps with different kinds of transparent backs

Non-biting Species	Common Name	2001 Total	Daily Max
Sarcophagidae	Flesh flies	1522	65
Anthomyiidae	Anthomyiid flies	1096	159
Calliphoridae	Blow flies	807	65
Lepidoptera		807	24
Moths		621	19
Butterflies		186	14
Hymenoptera		339	15
Wasps	Various	133	7
Ichneumonidae	Ichneumon wasps	97	3
Apoidea	Bees	59	7
Vespidae	Yellowjacket wasps	50	3
Syrphidae	Hover flies	272	10
Non-biting Muscidae	"House" flies	221	19
Mydaeinae		129	17
Not Identified		106	11
Phaoiinae		40	3
Muscinae		4	1
Fannia spp.		4	2
Musca autumnalis	Face fly	3	1
Dolichopodidae	Long-legged flies	146	11
Tilupidae	Crane flies	141	8
Coleoptera	Beetles	102	10
Tephritidae	Fruit flies	108	10
Nematocera	Midges, gnats, etc.	67	7
Asilidae	Robber flies	64	12
Scatophagidae	Scatophagid flies	51	5
Hemiptera	Bugs	47	8
Otitidae	Picture-winged flies	42	4
Tachinidae	Tachinid flies	34	3
Brachycera	Higher flies	32	6
Homoptera	Hoppers	16	4
Neuroptera	Lacewings	9	1
Bombylidae	Bee flies	4	1
Stratiomyidae	Soldier flies	3	1
Therevidae	Stiletto flies	3	1
Xylomyidae	Xylomyid flies	2	2
Orthoperta	Grasshopper	1	1

Effect of Trap Height

I did a simple test in 2001 when tabanids were abundant to document the effect of increasing trap height by about 50 cm relative to the standard practice of setting Nzi traps near the ground. This is about as high as practical for working without a ladder, and is typical of the height at which many tabanid traps are set. From 3 July to 5 August, I moved an unbaited Nzi trap up and down on random occasions, generating 17 days of data for each trap height.

Total catch of Tabanidae was nearly identical at the two heights (12.8 per day at 50 cm height, 12.7 per day at 0 cm height). But, there was a qualitative change in species composition, with an increase in the catch of Chrysops aberrans and a decrease in the catch of Tabanus similis at 50 cm. Results are shown below. I have yet to pursue this type of basic empirical work in more detail.

Ground Level (N=204)

Ground Level

50 cm Height (N=216)

50 cm Height

Capturing Male Tabanids

The Nzi trap catches very few male tabanids. This is typical of conventional traps for biting flies, as only females feed on blood and hence are actively seeking hosts. Males can, however, be collected conveniently by placing suitable sticky materials on the ground to mimic "pools of water" as per Hall et al. (1998). The problem with using this technique is the routine capture of other animals - e.g. you will capture lots of other insects, and may be unlucky enough to capture birds, shrews, the neighbour's cat, etc.

Hall, M.J.R., Farkas, R. & Chainey, J.E. (1998) Use of odour-baited sticky boards to trap tabanid flies and investigate repellents. Medical and Veterinary Entomology 12, 241-245.

I have not experimented much with this technique, but did test it once at the right time and under the right weather conditions, and obtained excellent results. On June 10, 2007, I placed a triangular translucent blue panel of plexiglass (Rohm Haas #2424) on the ground in my back yard in Russell at a time when Hybomitra lasiophthalma were abundant. I covered it in transparent sticky sheeting from Olson Products. The day was ideal - hot and sunny throughout. Between 11 am and 7 pm, I caught 55 male + 12 female H. lasiophthalma, 4 male Chrysops, and 78 female snipe flies. For comparison, in six years of routine work prior to this date, I had caught exactly one male H. lasiophthalma in a Nzi trap.